Not Applicable
Not Applicable
1. Field of the Invention
The present invention relates to hydraulic valves, and more particularly to assemblies having a common monolithic block in which a plurality of individually operable valves are formed.
2. Description of the Related Art
Construction equipment have movable members which are operated by hydraulic cylinder/piston arrangements. For example, a skid steer loader has a boom that is used to raise and lower an implement, such as a bucket for moving dirt. Hydraulic actuators are provided for raising and lowering the boom and for tilting the implement with respect to the boom. An additional hydraulic circuit often is provided for auxiliary equipment.
The flow of fluid to and from each hydraulic actuator typically is controlled by a spool valve which in turn is controlled by a pilot valve. In this installation, a common valve body, known as a monolithic block, or monoblock, has a plurality of bores extending between two opposing surfaces, a separate control spool is received in each bore. Movement of the control spool opens and closes passages between the actuator and hoses that connect to a pump and a tank. Other hydraulic lines are attached to the openings at each end of the bores. These hydraulic lines lead to the pilot valves located within the cab of the skid steer loader. When the user desires to activate a particular function on the equipment, the pilot valve associated with that function is operated to vary the hydraulic pressure applied to the ends of the related control spool. Increasing the pressure at one end of the bore, causes the spool to move toward the other end which positions the spool to open a passage between the pump and a work port connected to the actuator for the desired function. Applying pressure to the other end of the bore moves the spool valve in the opposite direction to a open a passage between the work port and the tank of the hydraulic system. When the pilot valve is released, both ends of the bore are connected to the tank thereby causing the control spool to assume a center position. In the case of a hydraulic cylinder, bidirectional movement of a more complex control spool connects one cylinder chamber to the pump or tank and the other cylinder chamber to the other one of the pump or tank.
As noted previously, a plurality of control spools are contained in bores in the monolithic block. Often it is difficult to connect all the various hydraulic lines for the pump, the tank, each actuator, and the pilot valves to a compact valve assembly block. In addition, pressure relief valves and other mechanisms also have to be provided in the hydraulic circuits. As a consequence, mechanics-servicing the machinery often have difficulty in disconnecting and reconnecting the various hydraulic lines attached to the valve block.
There is a current trend with respect to construction equipment away from manually operated or hydraulically piloted valves toward electro-hydraulically controlled valves. Electrical control simplifies the hydraulic plumbing as control valves do not have to be located in or near the operator cab. This change in technology also facilitates computerized control of various machine functions, to either assist the operator or prevent dangerous conditions from occurring. This too has created difficulties in that the control of a given piece of equipment may be a combination of manually operated hydraulic circuits and electrically operated ones. This further complicates the arrangement of hydraulic valves.
A hydraulic valve assembly includes a compact body that has two primary sides and at least two opposing secondary sides extending between the primary sides. A plurality of valve bores extend between the two opposing secondary sides, and an inlet and an outlet for the assembly communicate with the valve bores. Each valve bore also communicates with a different pair of work ports that open through one primary side. The body further includes a plurality of first control ports each extending from the one primary side to one end of a different one of the plurality of valve bores, and a plurality of second control ports each extending from the same primary side to another end of a different one of the plurality of valve bores.
A separate control spool is located in each of the valve bores for controlling flow of hydraulic fluid between the work ports and the inlet and outlet. The control spool also defines a chamber at each end of the respective valve bore and each chamber communicates either a first control port or a second control port. A plurality of pilot pressure control elements each received in a different one of the first control ports and second control ports to define pressure in a respective chamber of an associated one of the plurality of valve bores. In the preferred embodiment of the valve assembly, each pilot pressure control element is either a fluid conduit or an electrically operated valve.
By applying pressure at one end or the other end of the bore, the spool is moves to different positions in the bore. This causes the spool to form various passages between the inlet and outlet and the two work ports coupled to that bore.